XRF (X-ray fluorescence) is a non-destructive analytical technique used to determine the elemental composition of materials. XRF analyzers determine the chemistry of a sample by measuring the fluorescent (or secondary) X-ray emitted from a sample when it is excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays (“a fingerprint”) that is unique for that specific element, which is why XRF spectroscopy is an excellent technology for qualitative and quantitative analysis of material composition.
The X-ray fluorescence process
- A solid or a liquid sample is irradiated with high energy X-rays from a controlled X-ray tube.
- When an atom in the sample is struck with an X-ray of sufficient energy (greater than the atom’s K or L shell binding energy), an electron from one of the atom’s inner orbital shells is dislodged.
- The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom’s higher energy orbital shells.
- The electron drops to the lower energy state by releasing a fluorescent X-ray. The energy of this X-ray is equal to the specific difference in energy between two quantum states of the electron. The measurement of this energy is the basis of XRF analysis
Interpretation of XRF spectra
Most atoms have several electron orbitals (K shell, L shell, M shell, for example). When X-ray energy causes electrons to transfer in and out of these shell levels, XRF peaks with varying intensities are created and will be present in the spectrum, a graphical representation of X-ray intensity peaks as a function of energy peaks. The peak energy identifies the element, and the peak height/intensity is generally indicative of its concentration.
How is XRF used in industries?
Handheld XRF Analyzers identify alloys, detect tramp elements, deliver geochemical data, analyze precious metals, and determine coating weight and plating thickness, to ensure material chemistry specifications are met.
- Oil and gas—for positive material identification (PMI) of piping material, which is critical where flow accelerated corrosion, or sulfidic corrosion, is a concern
- Metal fabricating—for non-destructive elemental analysis to ensure that no incorrect or out-of-specification metals or alloys enter the manufacturing process
- Automotive & aerospace—for incoming inspection and quality control of metallic and coated parts
- Scrap metal recycling—for fast and accurate sorting of scrap metals, which is essential to enhance both workflow efficiency and profitability
- Precious metal recycling—for accurately determining grade of precious metals and to prevent deleterious metals from entering the recycling process
- Mining & exploration—for quickly identifying and recovering the most economically viable resources
- Construction & environmental engineering—for screening risk assessment, hazardous site modeling, and remediation quality control
Is XRF Safe?
During the analysis, the analyzer emits a directed radiation beam when the tube is energized. Reasonable effort should be made to maintain exposures to radiation as far below dose limits as is practical. This is known as the ALARA (As Low as Reasonably Achievable) principle. Three factors will help minimize your radiation exposure: time, distance, and shielding.
While the radiation emitted from a portable or handheld XRF elemental analyzer is similar to the exposure received in a normal medical or dental X-ray, care must be taken to always point a handheld XRF analyzer directly at the sample and never at a person or a body part. Here are seven safety tips:
- Provide radiation safety training to operators
- Never aim the device at yourself or others when the primary beam (x-ray on) lights are illuminated
- Never hold samples during analysis
- Be aware of primary beam indicator lights
- Handle and use with respect
- Store securely – obey local storage requirements
- If you have a Safety Emergency, notify your Radiation Safety Officer (RSO) and analyzer vendor